The present invention relates to internal combustion engines, and more particularly to engines of the type having a cam lobe, rather than a conventional distributor shaft, for operating an ignition system of the engine.
Ignition systems for the majority of internal combustion engines include a distributor unit having a rotatably mounted distributor shaft that is geared to a crank shaft of the engine, the distributor shaft extending from a distributor housing and having a rotor in the housing for sequentially defining a high-voltage electrical path to each spark plug of the engine. Traditionally, a set of electrical breaker points that are operated by a cam on the distributor shaft within the housing periodically interrupt a low-voltage primary circuit for properly timing activation of the high-voltage electrical circuitry. Typically, the points are provided in an assembly having a radial adjustment for defining a point gap and corresponding duty cycle or dwell angle of the primary circuit. The breaker point assembly is also mounted on a breaker plate having vacuum-actuated rotational movement for defining a variable vacuum advance. Similarly, the cam for actuating the breaker points is rotatably mounted on the distributor shaft and controlled relative thereto by a centrifugal advance mechanism. Thus dynamic ignition timing is variably responsive to manifold vacuum and the rotational speed of the engine, overall adjustment of the ignition timing being further effected by rotational adjustment of the distributor housing relative to the crank case or other stationary structure of the engine.
A relatively recent development is the substitution of magnetically activated solid-state circuitry for the breaker points. See, for example, U.S. Pat. No. 3,906,920 to Hemphill.
In another class of conventional internal combustion engines typically used in stationary power plants and mobile refrigeration units, the engine is operated at nearly constant speed and loading. Consequently, the vacuum and centrifugal advance mechanisms are usually omitted in order to save manufacturing and maintenance costs. In one variation of this class, a magnet or other trigger device is fixably mounted to the crankshaft or flywheel of the engine, and a magnetic pick-up coil or other sensor is mounted to the crank case or other fixed location. A problem with this configuration is that maintenance is difficult, particularly when the moving parts of the engine are completely enclosed. In such cases, the crankcase must be dismantled in order to perform routine maintenance, resulting in unwanted expense and delay. Moreover, the timing of the ignition is difficult to adjust because of the same limited accessibility. In another variation of this class, conventional breaker points are used, the breaker points being operated by a push rod that is actuated from within the crank case by a rotating cam member. Although push rod actuated ignition systems for such applications are inexpensive to produce because the conventional distributor housing shaft is not used, they are subject to the limitations and disadvantages that are associated with conventional breaker points. For example, the breaker points are subject to mechanical wear and arc-induced erosion, particularly when the points directly interrupt the primary circuit current of the ignition. This problem is exacerbated by the limited availability of replacement parts for special purpose engines. Further, the use of solid-state circuitry for permitting "dry-circuit" operation of the breaker points is undesirably expensive in that there is typically no convenient location for inexpensively mounting such circuitry because the breaker points themselves occupy a relatively large proportion of the available space. Moreover, even with such solid-state circuitry, the mechanical wear of the breaker point assembly is not eliminated.
Modern solid-state ignition technology of the prior art has not been applied to eliminate the breaker point assembly from push rod actuated ignition systems. This is because the modern solid-state systems each require a rotating member for repetitively producing or interrupting a magnetic field or other form of radiation.
Thus there is a need for a push rod actuated ignition system that completely eliminates the use of breaker points, that provides conveniently adjustable ignition timing, that is reliable and inexpensive to maintain.